Goethite is a major component in many mineral processing operations. Its presence can have adverse effects on solid/liquid separations. To understand the interactions between goethite surfaces and their influence on particle flocculation, the anionic polymer flocculants ammonium polyacrylate (NHPA), hydrolysed polyacrylamide (PHPA), and hydroxamic polyacrylamide (HXPA) were studied using a combination of atomic force microscopy (AFM), floc structure analyses, and settling tests. The floc settling velocity related to the different flocculants had the following order: NHPA > HXPA > PHPA. The different floc sizes indicated many small and large sized flocs formed with NHPA and PHPA, while monomodal medium sized flocs formed with HXPA. The mass fractal dimension values showed that more compact flocs were formed with HXPA than the other flocculants. The direct force measurements without flocculants confirmed that the goethite surfaces strongly repel each other in alkaline solutions, which agrees with DLVO theory for similarly charged surfaces. The various interactions measured with different flocculants can be related to their molecular structures and molecular weights. The incubation of NHPA at various pH values resulted in long-range adhesion after surface contact with multiple elastic minima, indicating strong adsorption and an expanded molecular conformation for the adsorbed flocculant. The strong elastic minima and long-range adhesion for HXPA indicated a strong adsorption of 2 this hydroxamic flocculant, consistent with the flocculation performance. The force interactions support the results of the settling tests and floc structures well, and AFM could be a good method for studying the relationship between surface interactions and particle flocculation in polymer flocculants.
A study on selective chelating precipitation of palladium metal from real electroplating wastewater using chitosan and its water-soluble derivative was conducted. The pH parameter, the concentrations of chitosan and its water-soluble derivative and the chelating precipitation time were experimentally investigated, and the optimum conditions were determined. The results revealed that both chitosan and its water-soluble derivative acted as chelating precipitation agents. Rapid chelating precipitation occurred when chitosan was added to real electroplating wastewater containing the chitosan derivative, thereby improving removal efficiency of palladium in different forms up to 95% under the optimum condition of 0.2 g/L chitosan and 0.16 mg/L derivative at pH 2.5. Then, dissolution experiments showed that chelating precipitation products could be dissolved in aqua regia. Additionally, selective chelating precipitation of palladium by chitosan and its derivative was characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Thus, it can be concluded that the combined utilization of chitosan and its water-soluble derivative is a promising approach method for the removal of different forms of palladium from real electroplating wastewater.
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